THE SCIENCE OF VOLCANOES.

Otago Daily Times, Issue 12392, 30 June 1902, Page 2

THE SCIENCE OF VOLCANOES.

THEIR CAUSIi. AND METHODS OF ACTION. (Daily Mail.) > A candlo that lias nearly ran its course, when its period of continuous light-giving is near its end, begins to splutter and evinces the oxisten'ce still of a little remaining energy in the spasmodic waning and outbursts of its dying light. Our world, geologically considered, is a dying_ one, and the energy of its internal heat is nearly spent; but it is not quite dead, and now and then it gives evidence of still great forces pent up within it by spasmodic and violent outbursts of volcar.io and seismic outbursts, silcli as that which overwhelmed Pompeii and Horeulaneum long years- ago and St. Pierre to-day. Something like 100,000,000 years ago tho world on which we lived iv« a molten globe, like the sun to-day, though on a smaller scale, and its surfaco was the scene of vast and prodigious displays of volcanic energy. All over the surfaco of tho globe, more plentiful along certain tracts than elsewhere, tho remains of ancient volcanoes are to bo found. Some of these, judging by their probable sizo, must have been tlio scat of a volcanic activity in comparison with which those of tho historic period sink into insignificance. Tiie World's Volcanic Coxes. One of the most terrible of volcanic outbursts that nas occurred within the historical period is that of a volcanic cone callcd l'apandayang, in Java, in the year 1772. This cone, before the eruption, was 9000 ft in height, and during a single nitrht, so violent was the outburst, that ita top was blown away, and its height reduced to 5000 ft. The ashes and lava which were discharged from it fell upon tlio country for many miles around, and buried no less than 40 villages. An approximate estimate showed that during, the course of a single night something like 30,003,000.000 cubio feet of materials were discharged from, its vent. Some of tho largest of the volcanic cones which are still active, or were but recently so, are those of the mountain of Teneriffe, iu the Canaries, which rises as a vast pyramidal mass 12,175 ft high; of Etna, 10,870 ft, with a base 91 miles in circumference; and in Ecuador, in South America, the gigantic peaks of Oliimborazo and Cotopaxi, 2d,oooft' and 28.000 ft respectively. above tho sea level of the Pacific, and the, summits ot which liavo never been readied bv'man. These are colossal mountains, which have been built up during millions of years by the accumulations of volcanic ashes and lava of successive eruptions. Elsewhere, in other.parts of the world, there liavo been similar giants among volcanoes, and the boliday tripper when he vis-its the Island of Skye. treads on thedinsal wreck of a once gigantic volcano, which .thundered forth its ashes and poured out its molten streams of lava in a period of the world's history, formed by geologista tlio Tertiary T'poch, and which at a rough approximation may be dated at about 30,000,000 years ago. This ancient volcano originally had a diameter of 30 miles at its liase and a height of 15,000 ft. At the present time nothing but a few rounded domo-liko masses or rugged peaks, not more than 3000 ft in height, remain to tell the ctory of what must have been truly stupendous volcanic activity. Ben Nevis, the Sidlaws, the Pc-ntlands, the Ochils, and Arthur's Seat, just outside Edinburgh, are remnants of very ancient volcanoes, 50,000,000 years or so iu age, which once made Scotland a veritable •" reign of fire." 120 AeTivn Volcanoes In North and South Wales there are similar basal wrecks of what oncc wero gigantic volcanoes, and among them may bo mentioned Snowdon and Pader Idrir. Many of the higher peaks of the Lake District, of tlio Wrckin Chain, in Shropshire, of Oliarnwood Forest, and of Dartmoor, in Devonshire, are the silent remnant? of British volcanoes that must once have exhibited volcanic activity on the grandest scale, and have rivalled in size and extent tho mighty giants of. Cotopaxi, Etna, and Teneriffe. Though it is not impossible, there is nbt much need to fear arccrudsscence of volcanic activity in these islands, for tho present centre of volcanic c-ncrgy is situated in the region of Java, very, far from Britain. Europe, as a matter of fact, is singularly, frco from active volcanoes, for on tho whole continent there is but one—that of Vesuvius. In the Mediterranean thero are no less than six—i.e., Stromboli and Vulcano, in the Lipari -Islands, Grali-im's Isle, off tho coast of Sicily , (now submarine),, Etna, in Sicily, and Santorin and Nisyros, in tho iEgean Sea. Africa contain? about 10, four stretching along the we3t coast and six along the cast, and 10 others. on wlands near, the coast. In north America there are 20, in Central America 25, and in South Amcrica 38, and these all occur along tho coast at tho base of tho great western mountain ranges of the Andes and Rocky Mountains. Asia eontains 24, of which, however, one-half aro confined to the peninsula of Kamsehatka, that stretches out into tho Pacific from the north-eastern corner of Japan. Tho great continents thus contain between them about 120 aotive volennocs, but it is a very significant fact that more than twice as many occur on oceanic islands scattered over various parts of tho \vorld, and so are surrounded on all sides by water. The Distribution of Volcanoes. One of the most remarkable features about the distribution of volcanoes is fho fact that they are arranged, on straight lines, which stretch across the world, and extend from eight to _ 15,000 miles in length. Ono of these lines is that marked by the whole western coast of North and South Amcrica, and along this some- of tho biggest volcanoes, like Teneriffo and Cotopaxi, occur. The existence of a largo number of big extinct volcanoes along it. show that in past pariods of the world's history this part of the globe was tho seat of very great activity. And in view of the terrible calamity that has stricken Martinique it is interesting to r.oto that- this island, together with Cuba, Hayti. Guadeloupe, Jamaica, St. Vincent, Trinidad, and St. Lucia lie on a line of volcanic activity that branches off from the main American one, a little south of Mexico, and thence strctches eastward this rango of islands as far as Guadeloupe, - the most eastern of the group. Tho other great line of volcanic activity strctches from Iceland through the Azores, the Canary Islands, tho Cape Verde Islands, Ascension and St. Helena, down nearly to the South Polar regions. Tho line which contains the greatest number of activo volcanoes-, however, is that which starts from the north-eastern comer of Japan, passes southwards through Tokio to tile Philippines, Borneo. Sumatra, Java, and New Guinea, thenen is continued through the Now Hebrides. Fijian Islands, and New Zealand to Victoria- Land in the South Polar regions. Volcanoes a>:d Wateh. The volcanoes of the Mediterranean and of the eastern and western coasts of Africa are likewise all situated on a lino, so that ali the volcanoes of the world have this remarkable linear arrangement. It is aa though they were situated on lines of weakness in tho earth's crust, whoro, great fissures had allowed of the escape of tlio pentnp forccs from within. Another remarkable feature in conncction with volcanoes is their .proximity to tho great ocean basins. All the continental volcanoes lie along the coast line, and tho islandie ones are. of course, situated in tlio midst of water. This relation of volcanoes to the sea is very suggestive whon we remember that tlio explosive violence of a volcanic eruption is due to the escape of highly heated steam; in fact, in a sense, a 'voleanie eruption is like a steam boiler bursturn. Tho ;opular conception that a volcano iV a burning hill is erroneous, for fire does not occur during an eruptive discharge, nl'itlier is there any smoke. What has been mistaken for flame is tlio glow of the molton lava, and the dust mingled with steam at a Inn!,** cjnoko. A volcano need not he a hi'l at All; it is essentially a fissure thrmirh wli'ch suncr-l'eated steam, fragment." of r<M-!;, and lava are discharged with explosive vio'ence.